The Role of Exosomes in Bone Remodeling: Implications for Bone Physiology and Disease

Extracellular Vesicles in Pathophysiology: A Prudent Target That Requires Careful Consideration

Extracellular vesicles (EVs) are membrane-bound particles released by cells to perform multitudes of biological functions. Owing to their significant implications in diseases, the pathophysiological role of EVs continues to be extensively studied, leading research to neglect the need to explore their role in normal physiology. Despite this, many identified physiological functions of EVs, including, but not limited to, tissue repair, early development and aging, are attributed to their modulatory role in various signaling pathways via intercellular communication. EVs are widely perceived as a potential therapeutic strategy for better prognosis, primarily through utilization as a mode of delivery vehicle. Moreover, disease-associated EVs serve as candidates for the targeted inhibition by pharmacological or genetic means. However, these attempts are often accompanied by major challenges, such as off-target effects, which may result in adverse phenotypes. This renders the clinical efficacy of EVs elusive, indicating that further understanding of the specific role of EVs in physiology may enhance their utility. This review highlights the essential role of EVs in maintaining cellular homeostasis under different physiological settings, and also discusses the various aspects that may potentially hinder the robust utility of EV-based therapeutics.

Mesenchymal Stem Cell-Derived Extracellular Vesicles in Bone-Related Diseases: Intercellular Communication Messengers and Therapeutic Engineering Protagonists

Extracellular vesicles (EVs) can deliver various bioactive molecules among cells, making them promising diagnostic and therapeutic alternatives in diseases. Mesenchymal stem cell-derived EVs (MSC-EVs) have shown therapeutic potential similar to MSCs but with drawbacks such as lower yield, reduced biological activities, off-target effects, and shorter half-lives. Improving strategies utilizing biotechniques to pretreat MSCs and enhance the properties of released EVs, as well as modifying MSC-EVs to enhance targeting abilities and achieve controlled release, shows potential for overcoming application limitations and enhancing therapeutic effects in treating bone-related diseases. This review focuses on recent advances in functionalizing MSC-EVs to treat bone-related diseases. Firstly, we underscore the significance of MSC-EVs in facilitating crosstalk between cells within the skeletal environment. Secondly, we highlight strategies of functional-modified EVs for treating bone-related diseases. We explore the pretreatment of stem cells using various biotechniques to enhance the properties of resulting EVs, as well as diverse approaches to modify MSC-EVs for targeted delivery and controlled release. Finally, we address the challenges and opportunities for further research on MSC-EVs in bone-related diseases.

Highly Multiplexed, Efficient, and Automated Single-Cell MicroRNA Sequencing with Digital Microfluidics

Single-cell microRNA (miRNA) sequencing has allowed for comprehensively studying the abundance and complex networks of miRNAs, which provides insights beyond single-cell heterogeneity into the dynamic regulation of cellular events. Current benchtop-based technologies for single-cell miRNA sequencing are low throughput, limited reaction efficiency, tedious manual operations, and high reagent costs. Here, a highly multiplexed, efficient, integrated, and automated sample preparation platform is introduced for single-cell miRNA sequencing based on digital microfluidics (DMF), named Hiper-seq. The platform integrates major steps and automates the iterative operations of miRNA sequencing library construction by digital control of addressable droplets on the DMF chip. Based on the design of hydrophilic micro-structures and the capability of handling droplets of DMF, multiple single cells can be selectively isolated and subject to sample processing in a highly parallel way, thus increasing the throughput and efficiency for single-cell miRNA measurement. The nanoliter reaction volume of this platform enables a much higher miRNA detection ability and lower reagent cost compared to benchtop methods. It is further applied Hiper-seq to explore miRNAs involved in the ossification of mouse skeletal stem cells after bone fracture and discovered unreported miRNAs that regulate bone repairing.

Osteoblast-derived exosomes promote osteogenic differentiation of osteosarcoma cells via URG4/Wnt signaling pathway

Osteosarcoma is a primary malignant bone tumor. Although surgery and chemotherapy are the main treatment methods, the overall curative effect remains unsatisfactory. Therefore, there is an urgent need to develop new therapeutic options for osteosarcoma. In this study, the effect and molecular mechanism of osteoblast-derived exosomes on the treatment of osteosarcoma were evaluated. Human primary osteoblasts were cultured to observe the effects of osteoblast-derived exosomes on the osteogenic differentiation of osteosarcoma cells both in vitro and in vivo. Alizarin red staining and alkaline phosphatase detection were used to evaluate the degree of osteogenic differentiation, and immunofluorescence and Western blotting were used to detect protein expression. The results showed that osteoblast-derived exosomes effectively inhibited the proliferation of osteosarcoma cells and promoted their mineralization in vitro. The exosomes also significantly inhibited tumor growth and promoted tumor tissue mineralization in vivo. Osteoblast-derived exosomes upregulated the expression of bone sialoprotein, osteonectin, osteopontin, runt-related transcription factor 2, and Wnt inhibitory factor 1, downregulated the expression of cyclin D1, and suppressed the nuclear accumulation of β-catenin and promoted its phosphorylation in vitro and in vivo. However, these effects were significantly reversed by upregulated gene (URG) 4 overexpression. These findings suggest that osteoblast-derived exosomes could activate the osteogenic differentiation process in osteosarcoma cells and promote their differentiation by targeting the URG4/Wnt signaling pathway.

Nanotherapy for bone repair: milk-derived small extracellular vesicles delivery of icariin

Icariin (ICA) played an important role in the treatment of inflammatory bone defects. However, pharmacokinetic studies have shown that its poor bioavailability limited its application. In this context, we isolated bovine milk-derived sEV and prepared sEV-ICA to improve the osteogenic effect of ICA. In this study, we successfully constructed sEV-ICA. sEV-ICA was found to have significantly higher osteogenic efficiency than ICA in cell culture and cranial bone defect models. Mechanistically, bioinformatics analysis predicted that signal transducers and activators of transcription 5 (STAT5a) may bind to the GJA1 promoter, while luciferase activity assays and chromatin immunoprecipitation (ChIP) experiments confirmed that STAT5a directly binded to the GJA1 promoter to promote osteogenesis. We proved that compared with ICA, sEV-ICA showed a better effect of promoting bone repair in vivo and in vitro. In addition, sEV-ICA could promote osteogenesis by promoting the combination of STAT5a and GJA1 promoter. In summary, as a complex drug delivery system, sEV-ICA constituted a rapid and effective method for the treatment of bone defects and could improve the osteogenic activity of ICA.

Message in a bubble: the translational potential of extracellular vesicles

Extracellular vesicles (EVs) are small, membrane-enclosed vesicles released by cells into the extracellular milieu. They are found in all body fluids and contain a variety of functional cargo including DNA, RNA, proteins, glycoproteins and lipids, able to provoke phenotypic responses in cells, both locally and at distant sites. They are implicated in a wide array of physiological and pathological processes and hence have attracted considerable attention in recent years as potential therapeutic targets, drug delivery vehicles and biomarkers of disease. In this review we summarise the major functions of EVs in health and disease and discuss their translational potential, highlighting opportunities of - and challenges to - capitalising on our rapidly increasing understanding of EV biology for patient benefit.

Bone-Targeted Exosomes: Strategies and Applications

As the global population ages, bone-related diseases have increasingly become a major social problem threatening human health. Exosomes, as natural cell products, have been used to treat bone-related diseases due to their superior biocompatibility, biological barrier penetration, and therapeutic effects. Moreover, the modified exosomes exhibit strong bone-targeting capabilities that may improve efficacy and avoid systemic side effects, demonstrating promising translational potential. However, a review of bone-targeted exosomes is still lacking. Thus, the recently developed exosomes for bone-targeting applications in this review are focused. The biogenesis and bone-targeting regulatory functions of exosomes, the constructive strategies of modified exosomes to improve bone-targeting, and their therapeutic effects for bone-related diseases are introduced. By summarizing developments and challenges in bone-targeted exosomes, It is striven to shed light on the selection of exosome constructive strategies for different bone diseases and highlight their translational potential for future clinical orthopedics.

Hormone-Related and Drug-Induced Osteoporosis: A Cellular and Molecular Overview

Osteoporosis resulting from an imbalance of bone turnover between resorption and formation is a critical health issue worldwide. Estrogen deficiency following a nature aging process is the leading cause of hormone-related osteoporosis for postmenopausal women, while glucocorticoid-induced osteoporosis remains the most common in drug-induced osteoporosis. Other medications and medical conditions related to secondary osteoporosis include proton pump inhibitors, hypogonadism, selective serotonin receptor inhibitors, chemotherapies, and medroxyprogesterone acetate. This review is a summary of the cellular and molecular mechanisms of bone turnover, the pathophysiology of osteoporosis, and their treatment. Nuclear factor-κβ ligand (RANKL) appears to be the critical uncoupling factor that enhances osteoclastogenesis. In contrast, osteoprotegerin (OPG) is a RANKL antagonist secreted by osteoblast lineage cells. Estrogen promotes apoptosis of osteoclasts and inhibits osteoclastogenesis by stimulating the production of OPG and reducing osteoclast differentiation after suppression of IL-1 and TNF, and subsequent M-CSF, RANKL, and IL-6 release. It can also activate the Wnt signaling pathway to increase osteogenesis, and upregulate BMP signaling to promote mesenchymal stem cell differentiation from pre-osteoblasts to osteoblasts rather than adipocytes. Estrogen deficiency leads to the uncoupling of bone resorption and formation; therefore, resulting in greater bone loss. Excessive glucocorticoids increase PPAR-2 production, upregulate the expression of Dickkopf-1 (DKK1) in osteoblasts, and inhibit the Wnt signaling pathway, thus decreasing osteoblast differentiation. They promote osteoclast survival by enhancing RANKL expression and inhibiting OPG expression. Appropriate estrogen supplement and avoiding excessive glucocorticoid use are deemed the primary treatment for hormone-related and glucocorticoid-induced osteoporosis. Additionally, current pharmacological treatment includes bisphosphonates, teriparatide (PTH), and RANKL inhibitors (such as denosumab). However, many detailed cellular and molecular mechanisms underlying osteoporosis seem complicated and unexplored and warrant further investigation.

The impacts of exosomes on bone metastatic progression and their potential clinical utility

Bone is one of the most common sites of cancer metastasis. Once cancer metastasizes to the bone, the mortality rate of cancer patients dramatically increases. Although the exact mechanisms for this observation remain elusive, recent studies have revealed that the complex crosstalk between bone marrow microenvironment and bone metastatic cancer cells is responsible for the induction of treatment resistance. Consequently, bone metastasis is currently considered incurable. Bone metastasis not only impairs the patients' survival, but also negatively affects their quality of life by causing painful complications. It has recently been implicated the regulatory role of exosomes in cancer development and/or progression as a delivery biomaterial between cancer cells and tumor microenvironment. However, little is known as to how exosomes contribute to the progression of bone metastasis by impaction on the crosstalk between bone metastatic cancer cells and bone marrow microenvironment. Here, we highlighted the emerging roles of cancer-derived exosomes in (i) the process of dissemination and bone colonization of bone metastatic cancer cells, (ii) the enhancement of crosstalk between bone marrow microenvironment and bone metastatic cancer cells, (iii) the development of its resultant painful complications, and (iv) the clinical applications of exosomes in the bone metastatic setting.

•

Cancer-derived exosomes facilitate cancer dissemination and colonization to bone.

•

Cancer-derived exosomes are crucial for controlling bone metastatic phenotype.

•

Cancer-derived exosomes prime bone marrow microenvironment for further metastasis.

•

Cancer-derived exosomes are involved in development of cancer-induced bone pain.

•

Exosomes can be used as therapies and/or diagnostic tools for bone metastasis.

Advances of Mesenchymal Stem Cells Released Extracellular Vesicles in Periodontal Bone Remodeling

Extracellular vesicles (EVs) are nanoparticles that include exosomes, microvesicles, and apoptotic bodies; they interact with target cell surface receptors and transport contents, including mRNA, proteins, and enzymes into the cytoplasm of target cells to function. The biological fingerprints of EVs practically mirror those of the parental cells they originated from. In the bone remodeling microenvironment, EVs could act on osteoblasts to regulate the bone formation, promote osteoclast differentiation, and regulate bone resorption. Therefore, there have been many attempts wherein EVs were used to achieve targeted therapy in bone-related diseases. Periodontitis, a common bacterial infectious disease, could cause severe alveolar bone resorption, resulting in tooth loss, whereas research on periodontal bone regeneration is also an urgent question. Therefore, EVs-related studies are important for periodontal bone remodeling. In this review, we summarize the current knowledge of mesenchymal stem cell-EVs involved in periodontal bone remodeling and explore the functional gene expression through a comparative analysis of transcriptomic content.

Circulating Exosomes from Mice with LPS-Induced Bone Loss Inhibit Osteoblast Differentiation

Osteoimmunology focuses on the intermodulation between bone and the immune system. Lipopolysaccharide (LPS)-induced bone loss models are commonly used to investigate the interface between inflammation and osteoporosis. Circulating exosomes can regulate physiological and pathological processes through exosomal microRNAs and proteins. In this study, we observed reduced osteoblast number and bone formation in LPS-induced bone loss mice (LPS mice). Levels of circulating exosomes were increased by ~ twofold in LPS mice, and the expression of exosomal miRNAs was significantly changed. miRNAs (miRNA-125b-5p, miRNA-132-3p, and miRNA-214-3p) that were reported to inhibit osteoblast activity were significantly increased in the serum exosomes and bone tissues of LPS mice. Additionally, LPS-induced increases in exosomes significantly inhibited the osteogenic differentiation of MC3T3-E1 cells.

Skeletal and extraskeletal disorders of biomineralization

The physiological process of biomineralization is complex and deviation from it leads to a variety of diseases. Progress in the past 10 years has enhanced understanding of the genetic, molecular and cellular pathophysiology underlying these disorders; sometimes, this knowledge has both facilitated restoration of health and clarified the very nature of biomineralization as it occurs in humans. In this Review, we consider the principal regulators of mineralization and crystallization, and how dysregulation of these processes can lead to human disease. The knowledge acquired to date and gaps still to be filled are highlighted. The disorders of mineralization discussed comprise a broad spectrum of conditions that encompass bone disorders associated with alterations of mineral quantity and quality, as well as disorders of extraskeletal mineralization (hyperphosphataemic familial tumoural calcinosis). Included are disorders of alkaline phosphatase (hypophosphatasia) and phosphate homeostasis (X-linked hypophosphataemic rickets, fluorosis, rickets and osteomalacia). Furthermore, crystallopathies are covered as well as arterial and renal calcification. This Review discusses the current knowledge of biomineralization derived from basic and clinical research and points to future studies that will lead to new therapeutic approaches for biomineralization disorders.

Identification of the key exosomal lncRNAs/mRNAs in the serum during distraction osteogenesis

Background

Distraction osteogenesis (DO), a kind of bone regenerative process, is not only extremely effective, but the osteogenesis rate is far beyond ordinary bone fracture (BF) healing. Exosomes (Exo) are thought to play a part in bone regeneration and healing as key players in cell-to-cell contact. The object of this work was to determine whether exosomes derived from DO and BF serum could stimulate the Osteogenic Differentiation in these two processes, and if so, which genes could be involved.

Methods

The osteogenesis in DO-gap or BF-gap was evaluated using radiographic analysis and histological analysis. On the 14th postoperative day, DO-Exos and BF-Exos were isolated and cocultured with the jaw of bone marrow mesenchymal stem cells (JBMMSCs). Proliferation, migration and osteogenic differentiation of JBMMSCs were ascertained, after which exosomes RNA-seq was performed to identify the relevant gene.

Results

Radiographic and histological analyses manifested that osteogenesis was remarkably accelerated in DO-gap in comparison with BF-gap. Both of the two types of Exos were taken up by JBMMSCs, and their migration and osteogenic differentiation were also seen to improve. However, the proliferation showed no significant difference. Finally, exosome RNA-seq revealed that the lncRNA MSTRG.532277.1 and the mRNA F-box and leucine-rich repeat protein 14(FBXL14) may play a key role in DO.

Conclusions

Our findings suggest that exosomes from serum exert a critical effect on the rapid osteogenesis in DO. This promoting effect might have relevance with the co-expression of MSTRG.532277.1 and FBXL14. On the whole, these findings provide new insights into bone regeneration, thereby outlining possible therapeutic targets for clinical intervention.

Research Progress of Exosomes in Bone Diseases: Mechanism, Diagnosis and Therapy

With the global escalation of the aging process, the number of patients with bone diseases is increasing year by year. Currently, there are limited effective treatments for bone diseases. Exosome, as a vital medium in cell-cell communication, can mediate tissue metabolism through the paracrine transmission of various cargos (proteins, nucleic acids, lipids, etc.) carried by itself. Recently, an increasing number of researchers have proven that exosomes play essential roles in the formation, metabolism, and pathological changes of bone and cartilage. Because exosomes have the advantages of small size, rich sources, and low immunogenicity, they can be used not only as substitutes for the traditional treatment of bone diseases, but also as biomarkers for the diagnosis of bone diseases. This paper reviews the research progress of several kinds of cells derived-exosomes in bone diseases and provides a theoretical basis for further research and clinical application of exosomes in bone diseases in the future.

Exosomes in the Treatment of Pancreatic Cancer: A Moonshot to PDAC Treatment?

Pancreatic Ductal Adenocarcinoma (PDAC) constitutes a leading cause of cancer death globally. Its mortality remains unaltered despite the considerable scientific progress made in the fields of diagnostics and treatment. Exosomes comprise of small extracellular vesicles secreted by nearly all cells; their cargo contains a vast array of biomolecules, such as proteins and microRNAs. It is currently established that their role as messengers is central to a plethora of both physiologic and pathologic processes. Accumulating data have shed light on their contributions to carcinogenesis, metastasis, and immunological response. Meanwhile, the advancement of personalized targeted therapies into everyday clinical practice necessitates the development of cost-efficient treatment approaches. The role of exosomes is currently being extensively investigated towards this direction. This review aims to summarize the current pre-clinical and clinical evidence regarding the effects of exosomal applications in the timely diagnosis, prognosis, and therapeutic management of pancreatic cancer.

Bone Cell Exosomes and Emerging Strategies in Bone Engineering

Bone tissue remodeling is a highly regulated process balancing bone formation and resorption through complex cellular crosstalk between resident bone and microenvironment cells. This cellular communication is mediated by direct cell and cell–matrix contact, autocrine, endocrine, and paracrine receptor mediated mechanisms such as local soluble signaling molecules and extracellular vesicles including nanometer sized exosomes. An impairment in this balanced process leads to development of pathological conditions. Bone tissue engineering is an emerging interdisciplinary field with potential to address bone defects and disorders by synthesizing three-dimensional bone substitutes embedded with cells for clinical implantation. However, current cell-based therapeutic approaches have faced hurdles due to safety and ethical concerns, challenging their clinical translation. Recent studies on exosome-regulated bone homeostasis and regeneration have gained interest as prospective cell free therapy in conjugation with tissue engineered bone grafts. However, exosome research is still in its nascent stages of bone tissue engineering. In this review, we specifically describe the role of exosomes secreted by cells within bone microenvironment such as osteoblasts, osteocytes, osteoclasts, mesenchymal stem cell cells, immune cells, endothelial cells, and even tumor cells during bone homeostasis and crosstalk. We also review exosome-based osteoinductive functionalization strategies for various bone-based biomaterials such as ceramics, polymers, and metals in bone tissue engineering. We further highlight biomaterials as carrier agents for exosome delivery to bone defect sites and, finally, the influence of various biomaterials in modulation of cell exosome secretome.

Potential Effects of Exosomes and Their MicroRNA Carrier on Osteoporosis

Osteoporosis is a typical localized or systemic skeletal disease in the clinic, mainly characterized by the weakness of bone formation and the increase of bone resorption, resulting in the decrease of bone mineral density (BMD), and frequently occurs in postmenopausal women. With the growth of the aging population, the risk of osteoporosis or even osteoporotic fracture brings great economic pressure on society and families. Although anti-osteoporosis drugs have been developed, there are still some side effects in the treatment group. Hence, that is a compelling need for more reasonable therapeutic strategies. Exosomes are nanosized extracellular vesicles (EVs), secreted by virtually all types of cells in vivo, which play an important role in intercellular communication. Compared with conventional drugs and stem cells transplantation therapy, exosomes have apparent advantages of lower toxicity and immunogenicity. Exosomes contain many functional molecules, such as proteins, lipids, mRNAs, microRNAs (miRNAs), which can be transferred into recipient cells to regulate a series of signaling pathways and influence physiological and pathological behavior. In this review, we briefly summarize the current knowledge of exosomes and the therapeutic potential of exosomal miRNAs derived from mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, and macrophages in osteoporosis. Finally, a prospect of new treatment strategies for osteoporosis using new biomaterial scaffolds combined with exosomes is also given.

The Physiological and Pathological Role of Tissue Nonspecific Alkaline Phosphatase beyond Mineralization

Tissue-nonspecific alkaline phosphatase (TNAP) is a key enzyme responsible for skeletal tissue mineralization. It is involved in the dephosphorylation of various physiological substrates, and has vital physiological functions, including extra-skeletal functions, such as neuronal development, detoxification of lipopolysaccharide (LPS), an anti-inflammatory role, bile pH regulation, and the maintenance of the blood brain barrier (BBB). TNAP is also implicated in ectopic pathological calcification of soft tissues, especially the vasculature. Although it is the crucial enzyme in mineralization of skeletal and dental tissues, it is a logical clinical target to attenuate vascular calcification. Various tools and studies have been developed to inhibit its activity to arrest soft tissue mineralization. However, we should not neglect its other physiological functions prior to therapies targeting TNAP. Therefore, a better understanding into the mechanisms mediated by TNAP is needed for minimizing off targeted effects and aid in the betterment of various pathological scenarios. In this review, we have discussed the mechanism of mineralization and functions of TNAP beyond its primary role of hard tissue mineralization.

Circulating microRNAs from the mouse tibia fracture model reflect the signature from patients with complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) often results from an initial trauma that later produces a disproportionate amount of pain. The mechanisms underlying CRPS have been studied using a tibia fracture model (TFM) in rodents because this model closely mimics symptoms and has several molecular correlates observed in patients with CRPS.

OBJECTIVE

Here, we determined whether the TFM has alterations in circulating microRNAs (miRNAs) and cytokines transported by small extracellular vesicles (sEVs) that faithfully model previously reported miRNA alterations from patients with CRPS.

METHODS

We isolated and characterized serum-derived sEVs from mice 3 weeks after fracture when symptoms such as pain hypersensitivity develop. Whole-transcriptome profiling was used to determine sEV miRNAs, and Bio-Plex Pro Mouse Cytokine 23-plex assay was used to measure cytokines. Differentially expressed miRNAs from TFM were compared with previously reported circulating miRNA alterations from patients with CRPS.

RESULTS

Although sEV cytokine levels were unchanged, there were significant changes in sEV miRNA profiles. Differentially expressed miRNAs from TFM sEVs significantly overlapped with those previously reported in patients with CRPS. Of the 57 sEV miRNAs dysregulated in the TFM, 30 were previously reported in patients with CRPS compared with healthy control donors both in sEVs and 23 in whole blood.

CONCLUSIONS

These findings enhance the validity of TFM as a model for CRPS and suggest that specific miRNA dysregulation may be a shared feature of CRPS and the TFM. These dysregulated miRNAs could help identify mechanistic targets or serve as biomarker candidates for both diagnosis and treatment responses in clinical trials.

Effect and mechanism of propranolol on promoting osteogenic differentiation and early implant osseointegration

The present study aimed to investigate the effect of β‑receptor blocker propranolol on early osseointegration of pure titanium implants and the underlying molecular regulatory mechanisms. An implant osseointegration model using the tibial metaphysis of New Zealand rabbits was established. The rabbits were divided into control and low‑, medium‑ and high‑dose propranolol groups. The formation of implant osseointegration was detected by X‑ray scanning. Mesenchymal stem cells (MSCs) and osteoblasts (OBs) were isolated and cultured in vitro, isoproterenol was supplemented to simulate sympathetic action and propranolol was subsequently administrated. The effect of propranolol on cell proliferation and osteogenic differentiation were assessed by EdU, flow cytometry, alizarin red staining and alkaline phosphatase (ALP) detection. The expression levels of bone morphogenetic protein (BMP)2, RUNX family transcription factor (RunX)2, collagen (COL)‑1, osteocalcin (OCN) and β2‑adrenergic receptor (AR) were detected by immunofluorescence, reverse transcription‑quantitative PCR and western blot assay. Propranolol effectively promoted implant osseointegration in vivo, facilitated proliferation of OBs, inhibited proliferation of MSCs and enhanced osteogenic differentiation of OBs and MSCs. The calcium content and ALP activity of cells treated with propranolol were markedly higher than in the control group. Propranolol also elevated mRNA and protein expression levels of BMP2, RunX2, COL‑1 and OCN in tissue and cells, and decreased the expression of β2‑AR. The present study demonstrated that the β‑receptor blocker propranolol promoted osteogenic differentiation of OBs and MSCs and enhanced implant osseointegration. The present study provided a novel insight into the application and regulatory mechanisms of propranolol.

Osteocyte exosomes accelerate benign prostatic hyperplasia development

Benign prostatic hyperplasia (BPH) is one of the most common diseases in elderly men. BPH patients exhibit an increased risk of vertebral and hip fractures, which are most attributable to pre-existing osteoporosis. However, the relationship between BPH and osteoporosis is still unknown. Here we found that osteocytes, the most abundant bone cells, promoted BPH development by secreting exosomes. In vitro, osteocyte exosomes (OCY-Exo) directly promoted cell proliferation of a prostate epithelial cell line BPH-1 and a macrophage cell line RAW264.7, OCY-Exo also stimulated macrophage-induced proliferation of BPH-1 cells. In vivo, intramedullary injection of OCY-Exo accumulated in prostate. Intravenous administration of OCY-Exo exacerbated testosterone-induced BPH in C57BL/6J mice. Our study uncovers the role of OCY-Exo as a stimulator of BPH, suggesting a novel mechanism in bone-prostate communication.

The role of exosomal non-coding RNAs in aging-related diseases

Aging is a biological process caused by the accumulation of senescent cells with a permanent proliferative arrest. To the influence of aging on human life expectancy, there is essential for new biomarkers which possibly will assistance in recognizing age-associated pathologies. Exosomes, which are cell-secreted nanovesicles, make available a new biomarker detection and therapeutic approach for the transfer of different molecules with high capacity. Recently, non-coding RNAs (ncRNA) which are contained in exosomes have developed as important molecules regulating the complexity of aging and relevant human diseases. The discovery of ncRNA provided perceptions into an innovative regulatory platform that could interfere with cellular senescence. The non-coding transcriptome includes a different of RNA species, spanning from short ncRNAs (<200 nucleotides) to long ncRNAs, that are >200 bp long. Upgraded evidence displays that targeting ncRNAs possibly will influence senescence pathways. In this article, we will address ncRNAs that participated in age-related and cellular senescence diseases. Growing conception of ncRNAs in the aging process possibly will be responsible for new understandings into the improvement of age-related diseases and elongated life span.

[Experimental study on improvement of osteonecrosis of femoral head with exosomes derived from miR-27a-overexpressing vascular endothelial cells]

Objective

To investigate whether exosomes derived from miR-27a-overexpressing human umbilical vein endothelial cells (HUVECs)-exo (miR-27a) can promote bone regeneration and improve glucocorticoids (GC) induced osteonecrosis of femoral head (ONFH) (GC-ONFH).

Methods

The exo (miR-27a) were intended to be constructed and identified by transmission electron microscopy, nanoparticle tracking analysis, Western blot, and real-time fluorescent quantitative PCR (qRT-PCR). qRT-PCR was used to evaluate the effect of exo (miR-27a) in delivering miR-27a to osteoblasts (MC3T3-E1 cells). Alkaline phosphatase staining, alizarin red staining, and qRT-PCR were used to evaluate its effect on MC3T3-E1 cells osteogenesis. Dual-luciferase reporter (DLRTM) assay was used to verify whether miR-27a targeting Dickkopf WNT signaling pathway inhibitor 2 (DKK2) was a potential mechanism, and the mechanism was further verified by qRT-PCR, Western blot, and alizarin red staining in MC3T3-E1 cells. Finally, the protective effect of exo (miR-27a) on ONFH was verified by the GC-ONFH model in Sprague Dawley (SD) rats.

Results

Transmission electron microscopy, nanoparticle tracking analysis, Western blot, and qRT-PCR detection showed that exo (miR-27a) was successfully constructed. exo (miR-27a) could effectively deliver miR-27a to MC3T3-E1 cells and enhance their osteogenic capacity. The detection of DLRTM showed that miR-27a promoted bone formation by directly targeting DDK2. Micro-CT and HE staining results of animal experiments showed that tail vein injection of exo (miR-27a) improved the osteonecrosis of SD rat GC-ONFH model.

Conclusion

exo (miR-27a) can promote bone regeneration and protect against GC-ONFH to some extent.

Exosomes from Adipose-Derived Stem Cells Can Prevent Medication-Related Osteonecrosis of the Jaw

The treatment measures of medication-related osteonecrosis of the jaw (MRONJ) is a worldwide challenge in oral and maxillofacial surgery because of its unclear pathogenesis. Previous studies suggested that mesenchymal stem cells played important roles in promoting MRONJ lesion healing, but the detailed mechanisms were unknown. Increasing numbers of studies have demonstrated that exosomes derived from mesenchymal stem cells, especially adipose-derived stem cells, have key roles in stem cell-based therapies by accelerating bone remodeling, facilitating angiogenesis, and promoting wound healing. We hypothesized that exosomes derived from adipose-derived stem cells can prevent MRONJ by accelerating gingival healing and enhancing bone remodeling processes. Our results may provide a promising therapeutic option for MRONJ clinical therapy.

The role of microRNAs in bone development

Epigenetic regulation is critical for proper bone development. Evidence from a large body of published literature informs us that microRNAs (miRNAs) are important epigenetic factors that control many aspects of bone development, homeostasis, and repair processes. These small non-coding RNAs function at the post-transcriptional level to suppress expression of specific target genes. Many target genes may be affected by one miRNA resulting in alteration in cellular pathways and networks. Therefore, changes in levels or activity of a specific miRNA (e.g. via genetic mutations, disease scenarios, or by over-expression or inhibition strategies in vitro or in vivo) can lead to substantial changes in cell processes including proliferation, metabolism, apoptosis and differentiation. In this review, Section 1 briefly covers general background information on processes that control bone development as well as the biogenesis and function of miRNAs. In Section 2, we discuss the importance of miRNAs in skeletal development based on findings from in vivo mouse models and human clinical reports. Section 3 focuses on describing more recent data from the last three years related to miRNA regulation of osteoblast differentiation in vitro. Some of these studies also involve utilization of an in vivo rodent model to study the effects of miRNA modulation in scenarios of osteoporosis, bone repair or ectopic bone formation. In Section 4, we provide some recent information from studies analyzing the potential of miRNA-mediated crosstalk in bone and how exosomes containing miRNAs from one bone cell may affect the differentiation or function of another bone cell type. We then conclude by summarizing where the field currently stands with respect to miRNA-mediated regulation of osteogenesis and how information gained from developmental processes can be instructive in identifying potential therapeutic miRNA targets for the treatment of certain bone conditions.

Extracellular Vesicles in Musculoskeletal Pathologies and Regeneration

The incidence of musculoskeletal diseases is steadily increasing with aging of the population. In the past years, extracellular vesicles (EVs) have gained attention in musculoskeletal research. EVs have been associated with various musculoskeletal pathologies as well as suggested as treatment option. EVs play a pivotal role in communication between cells and their environment. Thereby, the EV cargo is highly dependent on their cellular origin. In this review, we summarize putative mechanisms by which EVs can contribute to musculoskeletal tissue homeostasis, regeneration and disease, in particular matrix remodeling and mineralization, pro-angiogenic effects and immunomodulatory activities. Mesenchymal stromal cells (MSCs) present the most frequently used cell source for EV generation for musculoskeletal applications, and herein we discuss how the MSC phenotype can influence the cargo and thus the regenerative potential of EVs. Induced pluripotent stem cell-derived mesenchymal progenitor cells (iMPs) may overcome current limitations of MSCs, and iMP-derived EVs are discussed as an alternative strategy. In the last part of the article, we focus on therapeutic applications of EVs and discuss both practical considerations for EV production and the current state of EV-based therapies.

Osteoporosis Is Characterized by Altered Expression of Exosomal Long Non-coding RNAs

Osteoporosis is a metabolic bone disease characterized by a decrease in bone mass and degradation of the bone microstructure, which increases bone fragility and risk of fracture. However, the molecular mechanisms of osteoporosis remain unclear. The current study attempts to elucidate the role of exosomal long non-coding RNA in the pathology of osteoporosis. Peripheral blood was collected from persons with (OP) or without (NC) osteoporosis, and the serum exosomes were extracted using ultra centrifugation process. Total RNA of exosomes was isolated, and the lncRNAs profiling was done using RNA-Seq experiments. In silico analysis resulted in identification of 393 differentially expressed (DE) lncRNAs in OP vs. NC, with 296 that were up-regulated and 97 were down-regulated. Bioinformatics analysis of potential target mRNAs of lncRNAs with cis-acting mechanism showed that mRNAs co-located with DE lncRNAs were highly enriched in osteoporosis-related pathways, including regulation of insulin secretion, activation of MAPK activity, cellular response to metal ions, fucosylation and proteolysis. Together these results suggest that lncRNAs of serum exosomes could play a significant role in development of osteoporosis and such information may be helpful in developing diagnostic markers and therapeutic modules for osteoporosis.

Osteogenic Effect of tsRNA-10277-Loaded Exosome Derived from Bone Mesenchymal Stem Cells on Steroid-Induced Osteonecrosis of the Femoral Head

Purpose

Steroids are known to inhibit osteogenic differentiation and subsequent bone formation in bone mesenchymal stem cells (BMSCs). However, little is known about the role of BMSC exosomes (Exos) and tRNA-derived small RNAs (tsRNAs) in steroid-induced osteonecrosis of the femoral head (SONFH). The objective of this study was to characterize the tsRNA expression profiles of plasma Exos collected from SONFH patients and healthy individuals using small RNA sequencing and further explore the effect of BMSC Exos carrying specific tsRNAs on osteogenic differentiation.

Materials and Methods

Based on insights from small RNA sequencing, five differentially expressed (DE) tsRNAs were selected for quantitative real-time polymerase chain reaction (qRT-PCR). The regulatory networks associated with interactions of the tsRNAs-mRNA-pathways were reconstructed. The osteogenesis and adipogenesis in BMSCs were detected via ALP and oil red O staining methods, respectively.

Results

A total of 345 DE small RNAs were screened, including 223 DE tsRNAs. The DE tsRNAs were enriched in Wnt signaling pathway and osteogenic differentiation. We identified five DE tsRNAs, among which tsRNA-10277 was significantly downregulated in plasma Exos of SONFH patients compared to that in healthy individuals. Dexamethasone-induced BMSCs were associated with an increased fraction of lipid droplets and decreased osteogenic differentiation, whereas BMSC Exos restored the osteogenic differentiation of that. After treatment of tsRNA-10277-loaded BMSC Exos, the lipid droplets and osteogenic differentiation ability were found to be decreased and enhanced in dexamethasone-induced BMSCs, respectively.

Conclusion

An altered tsRNA profile might be involved in the pathophysiology of SONFH. tsRNA-10277-loaded BMSC Exos enhanced osteogenic differentiation ability of dexamethasone-induced BMSCs. Our results provide novel insights into the osteogenic effect of BMSC Exos carrying specific tsRNAs on SONFH.

Synergic effects of decellularized bone matrix, hydroxyapatite, and extracellular vesicles on repairing of the rabbit mandibular bone defect model

BACKGROUND

Extracellular vesicles (ECV) and bone extracellular matrix (ECM) have beneficial effects on the treatment of some pathological conditions. The purpose of this study was to find the synergic effects of decellularized bone (DB) ECM and ECVs on the repair of rabbit.

METHODS

The quality of decellularized sheep bones was confirmed by H&E, Hoechst, DNA quantification, immunohistochemistry, histochemical staining, and scanning electron microscopy (SEM). Osteoblast-derived ECVs were evaluated by internalization test, Transmission electron microscopy, Dynamic light scattering, and flow cytometry for CD9, CD63, CD81 markers. The hydrogel containing DB and hydroxyapatite (HA) with or without ECVs was evaluated for osteoblast functions and bone repair both in vitro and in vivo.

RESULTS

The data indicated ECM preservation after decellularization as well as cell depletion. In vitro assessments revealed that mineralization and alkaline phosphatase activity did not improve after treatment of MG63 cells by ECVs, while in vivo morphomatrical estimations showed synergic effects of ECVs and DB + HA hydrogels on increasing the number of bone-specific cells and vessel and bone area compared to the control, DB + HA and ECV-treated groups.

CONCLUSIONS

The DB enriched with ECVs can be an ideal scaffold for bone tissue engineering and may provide a suitable niche for bone cell migration and differentiation.

Preparing the Bone Tissue Regeneration Ground by Exosomes: From Diagnosis to Therapy

Bone tissue engineering employs acellular scaffolds or scaffolds, along with cells and growth factors, to provide the mechanical support needed, as well as serve as a delivery vehicle for bioactive molecules to the injury sites. As tissue engineering continues to evolve, it has integrated two emerging fields: stem cells and nanotechnology. A paracrine factor that is found to be responsible for the major regenerative effect in stem cell transplantation is an extracellular vesicle called an 'exosome'. Recent advances in nanotechnology have allowed the 'exosome' to be distinguished from other extracellular vesicles and be polymerized into a well-defined concept. Scientists are now investigating exosome uses in clinical applications. For bone-related diseases, exosomes are being explored as biomarkers for different bone pathologies. They are also being explored as a therapeutic agent where progenitor cell-derived exosomes are used to regenerate damaged bone tissue. In addition, exosomes are being tested as immune modulators for bone tissue inflammation, and finally as a delivery vehicle for therapeutic agents. This review discusses recently published literature on the clinical utilization of exosomes in bone-related applications and the correlated advantages. A particular focus will be placed on the potential utilization of regenerative cell-derived exosomes as a natural biomaterial for tissue regeneration.

Exosomes in Nephropathies: A Rich Source of Novel Biomarkers

The biomarkers commonly utilized in diagnostic evaluations of kidney disease suffer from low sensitivity, especially in the early stages of renal damage. On the other hand, obtaining a renal biopsy to augment clinical decision making can lead to potentially serious complications. In order to overcome the shortcomings of currently available diagnostic tools, recent studies suggest that exosomes, cell-secreted extracellular vesicles containing a large array of active molecules to facilitate cell-to-cell communication, may represent a rich source of novel disease biomarkers. Because of their endocytic origin, exosomes carry markers typical for their parent cells, which could permit the localization of biochemical cellular alterations in specific kidney compartments. Different types of exosomes can be isolated from noninvasively obtained biofluids; however, in the context of kidney disease, evidence has emerged on the role of urinary exosomes in the diagnostic and predictive modeling of renal pathology. The current review summarizes the potential application of exosomes in the detection of acute and chronic inflammatory, metabolic, degenerative, and genetic renal diseases.